Simplify the following expression: $r = \dfrac{9q}{7} + \dfrac{q}{6}$
Explanation: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $7$ and $6$ $\lcm(7, 6) = 42$ $ r = \dfrac{6}{6} \cdot \dfrac{9q}{7} + \dfrac{7}{7} \cdot \dfrac{q}{6} $ $r = \dfrac{54q}{42} + \dfrac{7q}{42}$ $r = \dfrac{54q +7q}{42}$ $r = \dfrac{61q}{42}$